The Scanning Electron Microscope (SEM) is an external observation device for projecting an electron beam onto a sample and detecting reflected secondary electrons to display a picture with pixels having a luminosity proportional to the number of secondary electrons. An SEM may be used for external inspecting and measuring a line width of fine patterns and micro dimensions.
In a semiconductor fabrication process, a line width of a fine pattern of a semiconductor device may be measured using a scanning electron microscope. A conventional method for measuring a micro line width uses a picture to judge a similarity between an inspection pattern and a standard pattern (i.e., pattern matching). That is, an SEM image of a standard pattern is compared with an SEM image of a real inspection pattern by pixels. A line width is measured only when the inspection pattern is determined to be non-defective as a result of the comparison. That is, the line width is not measured when the inspection pattern is determined to be defective.
However, according to the conventional method for matching a pattern, a pattern that is within a permissible modification range of a process may be determined to be defective. In this case, the measuring of line width may not be performed even though the measuring should be performed.